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This paper summarizes a series of tests performed on strain hardening High-Performance Fiber-Reinforced Concrete (HPFRC) coupling beams with span length-to-depth ratios (ln/h) of 1.75 and 2.75. These tests show that incorporating HPFRC simplifies the detailing required to ensure a stable response of coupling beams subjected to earthquake induced displacement reversals. Results from five tests of precast coupling beams, three with ln/h = 1.75 and two with ln/h = 2.75, are reported herein. Strategies for embedding the precast HPFRC coupling beams into the structural walls without interfering with boundary element reinforcement were explored. Test results confirm that HPFRC can reliably confine diagonal reinforcement and ensure stable hysteresis behavior. HPFRC was also found to significantly increase shear strength, thereby forcing a flexurally dominated failure mode with modest stiffness degradation and excellent energy dissipation. A revised coupling beam design philosophy is outlined in order to ensure ductile flexural behavior.

Previous studies using pullout-type tests comprising monotonic, unidirectional cyclic, and reversed cyclic loads have shown that bond between reinforcing bars/prestressing strands and concrete can be significantly enhanced by replacing the conventional concrete with high-performance fiber-reinforced cement composites (HPFRCCs). This is attributed to the fact that, compared to plain concrete and conventional fiber-reinforced concrete (FRC), HPFRCCs exhibit a strain-hardening response under tension up to large strains, thereby preventing the concrete from deterioration under bond action. Pullout test results provide the bond stress versus slip relationship that can be considered the constitutive property of the steel-to-HPFRCC interface. Since the post-cracking tensile stress and strain of fiber-reinforced cement composites are the fundamental characteristics that distinguish them from conventional concrete, the HPFRC tensile stress-strain response obtained from direct tensile tests was used to derive the local bond stress-slip models presented in this paper. It is shown that the proposed models are more concise than previous models suggested for FRC and give good agreement with test results.

Parameterized material models for strain softening fiber-reinforced concrete are used to express closed-form solutions of moment-curvature response of rectangular cross sections. By utilizing crack localization rules, one can predict flexural response of a beam. A parametric study of post crack tensile strength in the strain softening model is conducted to demonstrate general behavior of deflection softening and deflection hardening materials. Uniaxial and flexural test results of several polymeric fiber-reinforced concrete mixtures are used to demonstrate the applicability of the algorithm to predict load-deflection responses. The data are compared with the ASTM International test Method C1599, which represents the residual strength of the sample after cracking has taken place. The simulations reveal that uniaxial tensile stress-strain relationship is under-predicted using the flexural response test results.

The synergy between self-consolidating concrete (SCC) and steel fiber-reinforced concrete (SFRC) technologies may yield, besides the well known and assessed characteristics of each single technology, several interesting peculiar advantages that can be fruitfully exploited by the construction industry, mainly in the field of precast construction. Better controlled fiber dispersion, improved fiber-matrix bond, and enhanced durability due to the higher compactness of the SCC matrix are among the most relevant issues to which the largest part of research efforts were dedicated in the very last decade. The robustness of self-consolidating steel fiber-reinforced concrete (SCSFRC), which relies on sound mix-design methodology and on effective dedicated quality control procedures, has been demonstrated to be crucial in order to achieve the above recalled advantages. This paper summarizes the most significant results of the research activity carried out by the authors in this field, furthermore underlying the outcomes with reference to structural applications.

This Symposium Publication contains 14 papers that were presented at technical sessions sponsored by ACI Committees 544 and 549, and Joint ACI-ASCE Committee 423 at the 2008 ACI Spring Convention in Los Angeles, CA. Topics covered in these papers include development, mechanical behavior, modeling and structural applications of fiber- reinforced concrete and thin laminate composites; repair and rehabilitation of reinforced and prestressed concrete members; and new developments in prestressed concrete bridges. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-272